Simplify logging UTC option to only show time

We probably almost never care about the date, but it takes a lot of
space. Remove it; if somebody needs the full time stamp including the
date, we could still add it with a new option.

common/utils/LOG/log.c

@@ -575,8 +575,7 @@ static inline int log_header(log_component_t *c,
       struct tm utc_time;
       if (gmtime_r(&t.tv_sec, &utc_time) == NULL)
         abort();
-      snprintf(timeString, sizeof(timeString), "%04d-%02d-%02d %02d:%02d:%02d.%06lu UTC ",
-               utc_time.tm_year + 1900, utc_time.tm_mon + 1, utc_time.tm_mday,
+      snprintf(timeString, sizeof(timeString), "[%02d:%02d:%02d.%06lu] ",
                utc_time.tm_hour, utc_time.tm_min, utc_time.tm_sec, t.tv_nsec / 1000);
     } else {
       snprintf(timeString, sizeof(timeString), "%lu.%06lu ",